[CentOS] slow usb hard disk performance.

Bryan J. Smith thebs413 at earthlink.net
Mon Dec 5 18:18:01 UTC 2005


Robert <kerplop at sbcglobal.net> wrote:
> I wasn't complaining, Bryan, simply responding.

I never assumed you were complaining.  I merely pointed out
that a find|cpio command isn't a good command to use for
benchmarking, and 8.8MBps wasn't unreasonable for it given
the additional head seeks of the command and bottlenecks of
the USB interface.  That's all.

> Actually, having moved from a DAT-2 drive

DDS-2 drives are rather slow, about 0.8MBps natively -- some
15 years old -- and only hold 4GB natively anyway.  You'd be
better off with a DVD-R drive today.  Even 1x DVD-R is
1.35MBps.  I typically get 8x DVD-R for around 10MBps native.

Now if you're talking a modern tape backup like LTO-3, then
it's hard to beat.  It's literally 150x faster than old
DDS-2, and can stream at rates like a 2 or even 4 disk RAID-0
set.  DLT and LTO are fairly reliable, although not the
ultimate (that goes to IBM's proprietary tape technology).

> to the USB-connected disk, I'm happy as a pig in sh*t 
> to be able to backup the whole thing unattended and have a
> reasonable expectation that the resulting wad of crud is
good!

The problem with tape backup is that it's not used
appropriately.  You should never backup directly to tape. 
You should at least buffer to disk.  But in reality, why does
everything have to go to tape in the first place?  That's the
common issue.  Stuff like daily backups really don't, and
even weekly backups are not always required.

At the same time, as much as fixed disk might have an
advantage in near-guaranteed backups, it does present an
issue when it comes to long-term retention.  The disaster
recovery schemes I've seen fail are the ones that were either
all tape-only or all disk-only -- the combination is most
effective, with disk as the immediate and primary, and tape
for off-lining longer-term.

Hence the new "killer app" of Virtual Tape Libraries.  
  http://www.samag.com/documents/sam0509a/  

> (I'm still gonna burn /boot, /root, /home and /etc to DVD
once
> a month, though.)

Yes, an effective disaster recovery ensures you can bring up
the system ASAP.  Having a bootable DVD is critical, and
typically why I make my root (/) partition 8GiB or less (so
it fits on a 4.35GiB DVD-R when compressed).



-- 
Bryan J. Smith                | Sent from Yahoo Mail
mailto:b.j.smith at ieee.org     |  (please excuse any
http://thebs413.blogspot.com/ |   missing headers)



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